Original question, I know. Though irach did say "published in two parts", and we can't go too much further back before "published" stops being a meaningful concept.

[jim] Yes, both parts first came out in print prior to 1700.

Just a wild stab at a windmill in the dark...

[jim] The baton...or lance in this case is passed to you...Don Quixote it is! The books Part I, El Ingenioso Hidalgo don Quijote de la Mancha and its sequel were published for Cervantes ten years apart, in 1604 and 1614 by publisher Francisco de Robles. Incidentally, Don Quixote was one of the first bestseller books for which pirated editions soon appeared in the marketplace. The fact that I considered Don Quixote as being a little more immortal than just famous for being a fictional character (in response to CdM's question) is that the personality trait adjective "quixotic" has also been derived from his name.

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Thank you, thank you. Another result of the first book's being so popular was a rash of what you might call "unofficial sequels", of rather poor quality. The second book was written in part as a response to these.
I hope it's not considered too much bad form to guess like that straight after having a question answered. Actually, I couldn't think of any two-part foreign language books of that sort of antiquity, and was about to guess the Bible, although certain that wasn't it, just to eliminate the possibility, when another candidate suddenly struck me.

Anyway, I am now thinking of an ABSTRACT, with ANIMAL and VEGETABLE connections. Game on.

'En un lugar de La Mancha, de cuyo nombre no quiero recordarme...' - I've always liked that as an opening line - it's the 'no quiero' that gives it its interest.

[Animal human] In one connection, specifically yes. In another connection, yes, but not specifically so. In a sense, specifically no.